Techniques for Combining Optical Beams into Shared Spatial Mode

ABSTRACT

A light detection and ranging (LiDAR) system includes a first optical source and a second optical source configured to emit respectively a first optical beam and a second optical beam that have opposite polarizations. The LiDAR system further includes a beam combining component to combine the first optical beam and the second optical beam into a single spatial mode optical beam and a first beam splitting component to split the single spatial mode optical beam into a plurality of single spatial mode optical beams.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.17/334,515 filed on May 28, 2021, which is a continuation of U.S. patentapplication Ser. No. 16/354,694, filed Mar. 15, 2019, now U.S. Pat. No.11,022,683 which claims priority to U.S. Provisional Patent ApplicationNo. 62/643,414, filed Mar. 15, 2018, the contents of which areincorporated herein by reference in their entirety.

TECHNOLOGICAL FIELD

The present disclosure relates generally to traditional light detectionand ranging (LiDAR) and, in particular, to LiDAR that providessimultaneous measurement of range and velocity across two dimensions.

BACKGROUND

Typical LiDAR systems are pulsed based (or direct detection) and theysimply cannot measure the range and velocity of the objectsimultaneously. Example implementations of the present disclosure arebased on a different kind of LiDAR system which is frequency modulated(FM). Typical FM LiDAR systems are bulky and large and suffer fromsignificant losses in the receive path. This leads into more poweroutput which is limited by eye safety or shorter ranges.

BRIEF SUMMARY

The present disclosure includes, without limitation, the followingexample implementations.

Some example implementations provide a light detection and ranging(LiDAR) system comprising: a first optical source and a second opticalsource configured to emit respectively a first optical beam and a secondoptical beam that have opposite polarizations; a first tap and a secondtap configured to split respectively the first optical beam and thesecond optical beam into a first high-power path optical beam and afirst low-power path optical beam, and a second high-power path opticalbeam and a second low-power path optical beam; a first polarization beamsplitter configured to combine the first high-power path optical beamand the second high-power path optical beam into a single spatial modeoptical beam; and at least one optical arrangement for at least onetarget, each optical arrangement including: lensing optics configured tolaunch the single spatial mode optical beam towards the target, andcollect light incident upon the target into a return path, the lightbeing collected into a return optical beam; a second polarization beamsplitter configured to split the return optical beam into a firstspatial mode optical beam and a second spatial mode optical beam; afirst mixer configured to mix the first spatial mode optical beam andthe first low-power path optical beam to produce an optical beam havinga first beat frequency, and a second mixer configured to mix the secondspatial mode optical beam and the second low-power path optical beam toproduce an optical beam having a second beat frequency; and a firstoptical detector and a second optical detector configured to detectrespectively the optical beam having the first beat frequency and theoptical beam having the second beat frequency, a range and velocity ofthe target being determinable from the first beat frequency and thesecond beat frequency.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the first optical detector and the second opticaldetector are each a balanced optical detector.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the LiDAR system further comprises an optical amplifierbetween the first polarization beam splitter and lensing optics, theoptical amplifier configured to amplify the single spatial mode opticalbeam.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the optical arrangement further includes at least oneoptical device configured to route the single spatial mode optical beamfrom the first polarization beam splitter to the lensing optics, androute the return optical beam from the lensing optics to the secondpolarization beam splitter.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the optical arrangement includes a polarization waveplate configured to convert polarization of the return optical beamcompared to the single spatial mode optical beam.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the lensing optics include distinct first and secondlensing optics configured to respectively launch the single spatial modeoptical beam towards the target, and collect the light incident upon thetarget into the return path, the light being collected into the returnoptical beam.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the LiDAR system further comprises: a third tap betweenthe first polarization beam splitter and the at least one opticalarrangement, the third tap configured to split the single spatial modeoptical beam into the single spatial mode optical beam and anothersingle spatial mode optical beam; and a local reference interferometerconfigured to receive the other single spatial mode optical beam, thelocal reference interferometer including: an optical splitter configuredto split the other respective single spatial mode optical beam into afirst part optical beam and a second part optical beam for propagationalong respectively a first path and a second path, the first path havinga propagation medium to give the first path a greater length than thesecond path; an optical combiner configured to combine the first partoptical beam and the second part optical beam from the first path andthe second path into a reference optical beam; and a third polarizationbeam splitter configured to split the reference optical beam into afirst reference optical beam and a second reference optical beam.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the LiDAR system is implemented with a circuit that iscompatible with current photonic integrated circuits.

Some example implementations provide a light detection and ranging(LiDAR) system comprising: a first optical source and a second opticalsource configured to emit respectively a first optical beam and a secondoptical beam that have opposite polarizations; a first tap and a secondtap configured to split respectively the first optical beam and thesecond optical beam into a first high-power path optical beam and afirst low-power path optical beam, and a second high-power path opticalbeam and a second low-power path optical beam; a first optical splitterand a second optical splitter configured to split respectively the firstlow-power path optical beam into multiple first low-power path opticalbeams, and the second low-power path optical beam into multiple secondlow-power path optical beams; a first polarization beam splitterconfigured to combine the first high-power path optical beam and thesecond high-power path optical beam into a single spatial mode opticalbeam; a third optical splitter configured to split the single spatialmode optical beam into multiple single spatial mode optical beams; andmultiple optical arrangements for multiple targets, each of the multipleoptical arrangements including: lensing optics configured to launch arespective single spatial mode optical beam of the multiple singlespatial mode optical beams towards a respective target of the multipletargets, and collect light incident upon the respective target into areturn path, the light being collected into a return optical beam; asecond polarization beam splitter configured to split the return opticalbeam into a first spatial mode optical beam and a second spatial modeoptical beam; a first mixer configured to mix the first spatial modeoptical beam and a respective first low-power path optical beam of themultiple first low-power path optical beams to produce an optical beamhaving a first beat frequency, and a second mixer configured to mix thesecond spatial mode optical beam and a respective second low-power pathoptical beam of the multiple second low-power path optical beams toproduce an optical beam having a second beat frequency; and a firstoptical detector and a second optical detector configured to detectrespectively the optical beam having the first beat frequency and theoptical beam having the second beat frequency, a range and velocity ofthe respective target being determinable from the first beat frequencyand the second beat frequency.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the first optical detector and the second opticaldetector are each a balanced optical detector.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the LiDAR system further comprises an optical amplifierbetween the first polarization beam splitter and the optical splitter,the optical amplifier configured to amplify the single spatial modeoptical beam.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, each of the optical arrangements further includes atleast one optical device configured to route the respective singlespatial mode optical beam from the optical splitter to the lensingoptics, and route the return optical beam from the lensing optics to thesecond polarization beam splitter.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the lensing optics include distinct first and secondlensing optics configured to respectively launch the respective singlespatial mode optical beam towards the target, and collect the lightincident upon the target into the return path, the light being collectedinto the return optical beam.

In some example implementations of the LiDAR system of any precedingexample implementation, or any combination of preceding exampleimplementations, the LiDAR system further comprises: a third tap betweenthe first polarization beam splitter and the multiple opticalarrangements, the third tap configured to split the single spatial modeoptical beam into the single spatial mode optical beam and anothersingle spatial mode optical beam; and a local reference interferometerconfigured to receive the other single spatial mode optical beam, thelocal reference interferometer including: a fourth optical splitterconfigured to split the other respective single spatial mode opticalbeam into a first part optical beam and a second part optical beam forpropagation along respectively a first path and a second path, the firstpath having a propagation medium to give the first path a greater lengththan the second path; an optical combiner configured to combine thefirst part optical beam and the second part optical beam from the firstpath and the second path into a reference optical beam; and a thirdpolarization beam splitter configured to split the reference opticalbeam into a first reference optical beam and a second reference opticalbeam.

Some example implementations provide a method of light detection andranging, the method comprising: emitting respectively a first opticalbeam and a second optical beam that have opposite polarizations;splitting respectively the first optical beam and the second opticalbeam into a first high-power path optical beam and a first low-powerpath optical beam, and a second high-power path optical beam and asecond low-power path optical beam; combining the first high-power pathoptical beam and the second high-power path optical beam into a singlespatial mode optical beam; and launching the single spatial mode opticalbeam towards the target, and collect light incident upon the target intoa return path, the light being collected into a return optical beam;splitting the return optical beam into a first spatial mode optical beamand a second spatial mode optical beam; mixing the first spatial modeoptical beam and the first low-power path optical beam to produce anoptical beam having a first beat frequency, and mixing the secondspatial mode optical beam and the second low-power path optical beam toproduce an optical beam having a second beat frequency; and detectingrespectively the optical beam having the first beat frequency and theoptical beam having the second beat frequency, a range and velocity ofthe target being determinable from the first beat frequency and thesecond beat frequency.

In some example implementations of the method of any preceding exampleimplementation, or any combination of preceding example implementations,the optical beam having the first beat frequency and the optical beamhaving the second beat frequency are detected by respectively a firstoptical detector and a second optical detector are each a balancedoptical detector.

In some example implementations of the method of any preceding exampleimplementation, or any combination of preceding example implementations,the method comprises a first polarization beam splitter combining thefirst high-power path optical beam and the second high-power pathoptical beam into the single spatial mode optical beam, and lensingoptics launching the single spatial mode optical beam towards thetarget, and collecting light incident upon the target into a returnpath, the light being collected into a return optical beam.

In some example implementations of the method of any preceding exampleimplementation, or any combination of preceding example implementations,the method further comprises an optical amplifier, between the firstpolarization beam splitter and lensing optics, amplifying the singlespatial mode optical beam.

In some example implementations of the method of any preceding exampleimplementation, or any combination of preceding example implementations,the method further comprises at least one optical device routing thesingle spatial mode optical beam from the first polarization beamsplitter to the lensing optics, and routing the return optical beam fromthe lensing optics to the second polarization beam splitter.

In some example implementations of the method of any preceding exampleimplementation, or any combination of preceding example implementations,the lensing optics include distinct first and second lensing opticsrespectively launching the single spatial mode optical beam towards thetarget, and collecting the light incident upon the target into thereturn path, the light being collected into the return optical beam.

In some example implementations of the method of any preceding exampleimplementation, or any combination of preceding example implementations,the method further comprises: splitting the single spatial mode opticalbeam into the single spatial mode optical beam and another singlespatial mode optical beam; and receiving the other single spatial modeoptical beam at a local reference interferometer, the local referenceinterferometer at least: splitting the other respective single spatialmode optical beam into a first part optical beam and a second partoptical beam for propagation along respectively a first path and asecond path, the first path having a propagation medium to give thefirst path a greater length than the second path; combining the firstpart optical beam and the second part optical beam from the first pathand the second path into a reference optical beam; and splitting thereference optical beam into a first reference optical beam and a secondreference optical beam.

These and other features, aspects, and advantages of the presentdisclosure will be apparent from a reading of the following detaileddescription together with the accompanying figures, which are brieflydescribed below. The present disclosure includes any combination of two,three, four or more features or elements set forth in this disclosure,regardless of whether such features or elements are expressly combinedor otherwise recited in a specific example implementation describedherein. This disclosure is intended to be read holistically such thatany separable features or elements of the disclosure, in any of itsaspects and example implementations, should be viewed as combinableunless the context of the disclosure clearly dictates otherwise.

It will therefore be appreciated that this Brief Summary is providedmerely for purposes of summarizing some example implementations so as toprovide a basic understanding of some aspects of the disclosure.Accordingly, it will be appreciated that the above described exampleimplementations are merely examples and should not be construed tonarrow the scope or spirit of the disclosure in any way. Other exampleimplementations, aspects and advantages will become apparent from thefollowing detailed description taken in conjunction with theaccompanying figures which illustrate, by way of example, the principlesof some described example implementations.

BRIEF DESCRIPTION OF THE FIGURE(S)

Having thus described example implementations of the disclosure ingeneral terms, reference will now be made to the accompanying figures,which are not necessarily drawn to scale, and wherein:

FIGS. 1, 2 and 3 illustrate respectively sawtooth, triangle andcounter-chirp modulation schemes for FM LiDAR, according to exampleimplementations of the present disclosure;

FIG. 4 illustrates a four-dimensional (4D) FM LiDAR system according toexample implementations;

FIGS. 5A and 5B illustrate reducing the fiber tip selection through aquarter-wave plate (QWP) for respectively fiber tip reflection andtarget reflection, according to example implementations;

FIG. 6 illustrates a bi-static design of a 4D FM LiDAR system, accordingto example implementations;

FIG. 7 illustrates a two-beam implementation for a 4D FM LiDAR system,according to example implementations;

FIG. 8 illustrates a 4D FM LiDAR system with an auxiliary range arm,according to example implementations; and

FIG. 9 illustrates a flowchart with various steps in a method of lightdetection and ranging, according to some example implementations.

DETAILED DESCRIPTION

Example implementations of the present disclosure propose a method tomeasure the range and velocity simultaneously without suffering majorlosses in the receive path and with a circuit that is compatible withcurrent photonic integrated circuits such as, but not limited to,silicon photonics, silica or programmable logic controller (PLC)processes.

Example implementations of the present disclosure are directed to amethod to construct an optical radar that is capable of simultaneousmeasurement for range and velocity measurement in a compact,mass-manufacturable fashion. Example implementations have application ina number of different contexts, including in sensing contexts such asthose in transportation, manufacturing, metrology, medical, security,and the like. For example, in the automotive industry, such a device canassist with spatial awareness for automated driver assist systems, orself-driving vehicles. Additionally, it can help with velocitycalibration of a moving vehicle without the need for a separate inertialmovement unit (IMU).

Example implementations of the present disclosure are based on FM LiDAR.A typical LiDAR system sends a pulse out and the range to target ismeasured by calculating the time it takes for the pulse to come back. InFM LiDAR systems, the power of the optical beam is kept constant whilethe beam is modulated in the frequency domain. A sawtooth modulation isshow in FIG. 1.

The range to target or velocity from the target is then measured bylooking at the beat frequency (Δf) between the outgoing beam and theincoming beam. The beat frequency is then used to estimate the range tothe target as follows:

$\begin{matrix}{{\Delta\; f} = {{\Delta\; f_{Range}} + {\Delta\; f_{Doppler}}}} & (1) \\{{Range} = {\Delta\; f_{Range}\frac{{cT}_{S}}{2\; B_{S}}}} & (2) \\{{Velocity} = {\Delta\; f_{Doppler}\frac{\lambda_{c}}{2}}} & (3)\end{matrix}$

where λ_(c)=c/f_(c), and Δf_(Range) and Δf_(Doppler) are the range beatand Doppler beat frequencies corresponding to stationary and movingobjects, respectively.

The main issue with the above theme is differentiating between the rangefrequency and Doppler frequency.

Another method to capture the range and velocity simultaneously is toimply a triangle modulation scheme (shown in FIG. 2). In this schemethere is an upsweep and a down sweep. In the event of the Doppler shift,the upsweep frequency and down sweep frequency would be:

$\begin{matrix}{{\Delta\; f_{up}} = {{\Delta\; f_{Range}} - {\Delta\; f_{Doppler}}}} & (4) \\{{\Delta\; f_{dn}} = {{\Delta\; f_{Range}} + {\Delta\; f_{Doppler}}}} & (5)\end{matrix}$

In that modulation scheme, the Doppler is simply the difference betweenthe up and down sweep frequency while the Range is the average of the upand down sweep frequency. However, the issue is that the assumption isthat the velocity is contact during the up and down sweep. In a dynamicenvironment this assumption does not hold and a different modulationscheme is needed.

To achieve improved measurements of range and velocity, a counter chirpmechanism is employed (shown in FIG. 3). In this mechanism there are twooutgoing beams: one beat note (Δf_(up)) is measuring range+Doppler andother (Δf_(din)) is measuring range—Doppler. Example implementations ofthe present disclosure provide a method to construct a system capable ofachieving 4D measurement at long range using a counter chirp mechanismor similar.

One example implementation of the present disclosure is shown in FIG. 4.This example implementation includes two optical beams (Source A andSource B) that are launched in opposite polarizations to the circuit.Suitable examples of optical sources include laser sources,light-emitting diodes (LEDs) and the like. One can mount these opticalsources on the same sub-mount or on separate one, and then tune eachoptical beam with a wave. Each optical beam could be tuned in a counterchirp fashion such as what is shown in FIG. 2. In some examples, morethan two optical beams are used. The two or more optical beams may befrom the same or separate and distinct optical sources.

Each beam is then split to create each own local oscillator and thenboth beams are combined into single waveguide using a polarization beamsplitter (PBS). This beam can then be amplified using an EDFA or SOA orbooster and then launched into the space using a polarizationinsensitive circulator.

The return path is then returned through the circulator and then goesthrough the PBS which splits the light into its original orthogonalrotations (representing light from Source A and Source B). Each of thesetwo beams is then mixed with its respective LO to generate the beatsignal.

More specifically, then, FIG. 4 illustrates a LiDAR system 400 accordingto example implementations of the present disclosure. As shown, theLiDAR system includes at least a first optical source 402 a and a secondoptical source 402 b (e.g., laser sources, LEDs) configured to emitrespectively a first optical beam 404 a and a second optical beam 404 bthat have opposite polarizations. The LiDAR system includes a first tap406 a and a second tap 406 b. The first tap is configured to split thefirst optical beam into a first high-power path optical beam 408 a, afirst low-power path optical beam 410 a, and a first polarization beamsplitter 412. The second tap is configured to split the second opticalbeam into a second high-power path optical beam 408 b and a secondlow-power path optical beam 410 b. The first polarization beam splitteris configured to combine the first high-power path optical beam 408 aand the second high-power path optical beam 408 b into a single spatialmode optical beam 414.

As also shown, the LiDAR system 400 includes at least one opticalarrangement 416 for at least one target 418. Each optical arrangementincludes lensing optics 420 configured to launch the single spatial modeoptical beam 414 towards the target, and collect light incident upon thetarget into a return path, the light being collected into a returnoptical beam 422. A second polarization beam splitter 424 is configuredto split the return optical beam into a first spatial mode optical beam426 a and a second spatial mode optical beam 426 b.

The optical arrangement 416 includes first mixer 428 a is configured tomix the first spatial mode optical beam and the first low-power pathoptical beam 410 a to produce an optical beam 430 a having a first beatfrequency, and a second mixer 428 b is configured to mix the secondspatial mode optical beam and the second low-power path optical beam 410b to produce an optical beam 430 b having a second beat frequency. Asshown, a first optical detector 432 a and a second optical detector 432b are configured to detect respectively the optical beam having thefirst beat frequency and the optical beam having the second beatfrequency. As explained above, the range and velocity of the target aredeterminable from the first beat frequency and the second beatfrequency.

In some examples, the first optical detector 432 a and the secondoptical detector 432 b are each a balanced optical detector. This mayreduce any optical power being discarded at the output of the mixers,although single channel detection can also work.

In some examples, the LiDAR system 400 further includes an opticalamplifier 434 between the first polarization beam splitter 412 andlensing optics 420, the optical amplifier configured to amplify thesingle spatial mode optical beam 414. And in some examples, the opticalarrangement 416 further includes at least one optical device configuredto route the single spatial mode optical beam 414 from the firstpolarization beam splitter 412 to the lensing optics 420, and route thereturn optical beam 422 from the lensing optics to the secondpolarization beam splitter 424. As shown, the optical device(s) includean optical circulator 436 and a polarization wave plate such as aquarter-wave plate (QWP) 438.

The addition of the optical amplifier 434 in the signal path is toamplify the outgoing beam and therefore increase the signal-to-noiseratio (SNR) at the output. Adding such an amplifier may create a verystrong signal at the fiber tip that could act as a strong return signaland increase the noise floor. For that reason, the QWP 438 may be placedafter the optical circulator 436, which essentially converts thepolarization of the return beam compared to the outgoing beam, as shownin FIGS. 5A and 5B. It converts the slow axis polarization to right-handcircular while the fast axis to left-hand circular. After these counterrotating circular polarizations hit the target 418, it flips it backcausing the return beam from the target to arrive at the orthogonalpolarization. These target signals are opposite to the fiber tipselection of that polarization. The mixing LO polarization is set tomatch the target polarization causing the signal from the fiber tip tobe much lower.

Shown in FIG. 6 is the implementation of a bi-static design for the 4DFM LiDAR system. This implementation decouples the outgoing beam pathfrom the returning collection path. In particular, FIG. 6 illustrates aLiDAR system 600 according to other example implementations of thepresent disclosure. The LiDAR system 600 shown in FIG. 6 is similar tothe LiDAR system 400 shown in FIG. 4. In FIG. 6, though, the lensingoptics 420 include distinct first and second lensing optics 420 a, 420b. The first lensing optics is configured to respectively launch thesingle spatial mode optical beam 414 towards the target 418. The secondlensing optics is configured to collect the light incident upon thetarget into the return path, the light being collected into the returnoptical beam 422. Also in FIG. 6, the optical device(s) include a firstQWP 438 a configured to route the single spatial mode optical beam 414from the first polarization beam splitter 412 to the first lensingoptics, and a second QWP 438 b configured to route the return opticalbeam 422 from the second lensing optics to the second polarization beamsplitter 424.

An additional method to improve the versatility and usefulness of such aLiDAR system is to illuminate one's surroundings using multiple beams.One way to achieve this is by building many separate systems andsynthesizing their data streams. Such a design is cost and resourceinefficient from a hardware perspective because every system requiresits own optical sources and amplifiers. FIG. 7 shows a schematic of animplementation that uses two outgoing beams in an effort to poolresources.

In particular, FIG. 7 illustrates a LiDAR system 700 according to yetother example implementations of the present disclosure. Similar tobefore, the LiDAR system includes first and second optical sources 402a, 402 b configured to emit respectively first and second optical beams404 a, 404 b that have opposite polarizations. The LiDAR system includesa first tap 406 a configured to split the first optical beam into afirst high-power path optical beam 408 a and a first low-power pathoptical beam 410 a. Similarly, a second tap 406 b is configured to splitthe second optical beam into a second high-power path optical beam 408 band a second low-power path optical beam 410 b.

The LiDAR system 700 of these example implementations includes a firstoptical splitter 740 a configured to split the first low-power pathoptical beam 410 a into multiple first low-power path optical beams 410a′. A second optical splitter 740 b is configured to split the secondlow-power path optical beam 410 b into multiple second low-power pathoptical beams 410 b′. A first polarization beam splitter 412 isconfigured to combine the first high-power path optical beam 408 a andthe second high-power path optical beam 408 b into a single spatial modeoptical beam 414. And a third optical splitter 742 is configured tosplit the single spatial mode optical beam 414 into multiple singlespatial mode optical beams 414′.

As also shown, the LiDAR system 700 includes multiple opticalarrangements 416 for multiple targets 418. Similar to before, each ofthe multiple optical arrangements includes lensing optics 420, a secondpolarization beam splitter 424, first and second mixers 428 a, 428 b,and first and second optical detectors 432 a, 432 b. The lensing opticsis configured to launch a respective single spatial mode optical beam414′ of the multiple single spatial mode optical beams towards arespective target of the multiple targets, and collect light incidentupon the respective target into a return path, the light being collectedinto a return optical beam 422.

The second polarization beam splitter 424 is configured to split thereturn optical beam 422 into a first spatial mode optical beam 426 a anda second spatial mode optical beam 426 b. The first mixer 428 a isconfigured to mix the first spatial mode optical beam and a respectivefirst low-power path optical beam 410 a′ of the multiple first low-powerpath optical beams to produce an optical beam 430 a having a first beatfrequency. The second mixer 428 b is configured to mix the secondspatial mode optical beam and a respective second low-power path opticalbeam 410 b′ of the multiple second low-power path optical beams toproduce an optical beam 430 b having a second beat frequency. And thefirst optical detector 432 a and second optical detector 432 b areconfigured to detect respectively the optical beam having the first beatfrequency and the optical beam having the second beat frequency, fromwhich a range and velocity of the respective target are determinable.

As also shown, in some examples, the LiDAR system 700 includes anoptical amplifier 434 between the first polarization beam splitter 412and the optical splitter 742, the optical amplifier configured toamplify the single spatial mode optical beam 414. Also, in someexamples, each of the optical arrangements 416 further includes at leastone optical device (e.g., optical circulator 436, QWP 438) configured toroute the respective single spatial mode optical beam 414′ from theoptical splitter 742 to the lensing optics 420, and route the returnoptical beam 422 from the lensing optics to the second polarization beamsplitter 424.

The above example implementations may assume a single mode or multimodewaveguide. Coupling light in such a waveguide may be lossy. Anotherpossible implementation to increase the mode coupling efficiency is toconstruct the circuit in free space optics.

In some examples, an auxiliary range arm may be added to any of theabove implementations to help with the any nonlinear corrections asdescribed in other media. One example is shown in FIG. 8.

In particular, FIG. 8 illustrates a LiDAR system 800 according to yetother example implementations of the present disclosure. The LiDARsystem 800 shown in FIG. 8 is similar to the LiDAR system 400 shown inFIG. 4, but it may be equally configured similar to the LiDAR system 700shown in FIG. 7. As shown in FIG. 8, the LiDAR system 800 includes athird tap 840 and a local reference interferometer 842. The third tap islocated between the first polarization beam splitter 412 and the opticalarrangement(s) 416, and configured to split the single spatial modeoptical beam 414 into the single spatial mode optical beam and anothersingle spatial mode optical beam. And the local reference interferometeris configured to receive the other single spatial mode optical beam.

The local reference interferometer 416 includes an optical splitter 844configured to split the other respective single spatial mode opticalbeam 414 into a first part optical beam 846 a and a second part opticalbeam 846 b for propagation along respectively a first path and a secondpath, with the first path having a propagation medium 848 to give thefirst path a greater length than the second path. An optical combiner850 is configured to combine the first part optical beam and the secondpart optical beam from the first path and the second path into areference optical beam 852. And third polarization beam splitter 854 isconfigured to split the reference optical beam 852 into a firstreference optical beam 852 a and a second reference optical beam 852 b.

Another variation of the system is to adjust the center wavelength ofthe two optical beams to provide different understanding of the targetmaterial (e.g., by looking at the difference in the return intensitybetween the two different wavelengths).

Even further, in some examples, a 2D scanner system may be added at theoutput of any example implementation to provide a true 4D map.

FIG. 9 illustrates a flowchart with various steps in a method 900 oflight detection and ranging, according to some example implementationsof the present disclosure. As shown at block 902, the method includesemitting respectively a first optical beam and a second optical beamthat have opposite polarizations. The method includes splittingrespectively the first optical beam and the second optical beam into afirst high-power path optical beam and a first low-power path opticalbeam, and a second high-power path optical beam and a second low-powerpath optical beam, as shown at block 904. The first high-power pathoptical beam and the second high-power path optical beam are combinedinto a single spatial mode optical beam, as shown at block 906. And thesingle spatial mode optical beam is launched towards the target, andlight incident upon the target into a return path is collected, thelight being collected into a return optical beam, as shown at block 908.

The method 900 includes splitting the return optical beam 422 into afirst spatial mode optical beam and a second spatial mode optical beam,as shown at block 910. The method includes mixing the first spatial modeoptical beam and the first low-power path optical beam to produce anoptical beam having a first beat frequency, and mixing the secondspatial mode optical beam and the second low-power path optical beam toproduce an optical beam having a second beat frequency, as shown atblock 912. The method further includes detecting respectively theoptical beam having the first beat frequency and the optical beam havingthe second beat frequency, as shown at block 914. Again, a range andvelocity of the target are determinable from the first beat frequencyand the second beat frequency.

The preceding description sets forth numerous specific details such asexamples of specific systems, components, methods, and so forth, inorder to provide a good understanding of several embodiments of thepresent disclosure. It will be apparent to one skilled in the art,however, that at least some embodiments of the present disclosure may bepracticed without these specific details. In other instances, well-knowncomponents or methods are not described in detail or are presented insimple block diagram format in order to avoid unnecessarily obscuringthe present disclosure. Thus, the specific details set forth are merelyexemplary. Particular embodiments may vary from these exemplary detailsand still be contemplated to be within the scope of the presentdisclosure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiments included inat least one embodiment. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.In addition, the term “or” is intended to mean an inclusive “or” ratherthan an exclusive or.

Although the operations of the methods herein are shown and described ina particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittent oralternating manner.

The above description of illustrated implementations of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific implementations of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize. The words “example” or“exemplary” are used herein to mean serving as an example, instance, orillustration. Any aspect or design described herein as “example” or“exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Rather, use of the words“example” or “exemplary” is intended to present concepts in a concretefashion. As used in this application, the term “or” is intended to meanan inclusive “or” rather than an exclusive “or”. That is, unlessspecified otherwise, or clear from context, “X includes A or B” isintended to mean any of the natural inclusive permutations. That is, ifX includes A; X includes B; or X includes both A and B, then “X includesA or B” is satisfied under any of the foregoing instances. In addition,the articles “a” and “an” as used in this application and the appendedclaims should generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Moreover, use of the term “an embodiment” or “one embodiment” or“an implementation” or “one implementation” throughout is not intendedto mean the same embodiment or implementation unless described as such.Furthermore, the terms “first,” “second,” “third,” “fourth,” etc. asused herein are meant as labels to distinguish among different elementsand may not necessarily have an ordinal meaning according to theirnumerical designation.

What is claimed is:
 1. A light detection and ranging (LiDAR) systemcomprising: a first optical source and a second optical sourceconfigured to emit respectively a first optical beam and a secondoptical beam that have opposite polarizations; a beam combiningcomponent to combine the first optical beam and the second optical beaminto a single spatial mode optical beam; and a first beam splittingcomponent to split the single spatial mode optical beam into a pluralityof single spatial mode optical beams.
 2. The LiDAR system of claim 1,further comprising: a first tap to split the first optical beam into afirst high-power path beam and a first low-power path optical beam; anda second tap to split the second optical beam into a first high-powerpath optical beam and a second low-power path optical beam.
 3. The LiDARsystem of claim 2, further comprising: a first optical arrangement toreceive and transmit a first single spatial mode optical beam of theplurality of single spatial mode optical beams.
 4. The LiDAR system ofclaim 3, wherein the first optical arrangement comprises: lensing opticsconfigured to direct the first single spatial mode optical beam of theplurality of single spatial mode optical beams towards a target, andcollect light incident upon the target into a return path, the lightbeing collected into a first return optical beam; a second beamsplitting component to split the first return optical beam into a firstspatial mode optical beam and a second spatial mode optical beam; and afirst optical detector and a second optical detector configured todetect respectively a first beat frequency of a combination of the firstspatial mode optical beam and the first low-power path optical beam anda second beat frequency of a combination of the second spatial modeoptical beam and the second low-power path optical beam.
 5. The LiDARsystem of claim 4, wherein the first optical detector and the secondoptical detector are each a balanced optical detector.
 6. The LiDARsystem of claim 4, wherein the first optical arrangement furtherincludes at least one optical device configured to route the singlespatial mode optical beam from the first beam splitting component to thelensing optics, and route the first return optical beam from the lensingoptics to the second beam splitting component.
 7. The LiDAR system ofclaim 4, wherein the lensing optics include distinct first and secondlensing optics configured to respectively transmit the single spatialmode optical beam towards the target, and collect the light incidentupon the target into the return path, the light being collected into thefirst return optical beam.
 8. The LiDAR system of claim 4, furthercomprising: a second optical arrangement to receive and transmit asecond single spatial mode optical beam of the plurality of singlespatial mode optical beams.
 9. A light detection and ranging (LiDAR)apparatus comprising: a first optical source and a second optical sourceconfigured to emit respectively a first optical beam and a secondoptical beam that have opposite polarizations; a beam combiningcomponent to combine the first optical beam and the second optical beaminto a single spatial mode optical beam; and a first beam splittingcomponent to split the single spatial mode optical beam into a pluralityof single spatial mode optical beams.
 10. The LiDAR apparatus of claim9, further comprising: a first tap to split the first optical beam intoa first high-power path beam and a first low-power path optical beam;and a second tap to split the second optical beam into a firsthigh-power path optical beam and a second low-power path optical beam.11. The LiDAR apparatus of claim 10, further comprising: a first opticalarrangement to receive and transmit a first single spatial mode opticalbeam of the plurality of single spatial mode optical beams.
 12. TheLiDAR apparatus of claim 11, wherein the first optical arrangementcomprises: lensing optics configured to direct the first single spatialmode optical beam of the plurality of single spatial mode optical beamstowards a target, and collect light incident upon the target into areturn path, the light being collected into a first return optical beam;a second beam splitting component to split the first return optical beaminto a first spatial mode optical beam and a second spatial mode opticalbeam; and a first optical detector and a second optical detectorconfigured to detect respectively a first beat frequency of acombination of the first spatial mode optical beam and the firstlow-power path optical beam and a second beat frequency of a combinationof the second spatial mode optical beam and the second low-power pathoptical beam.
 13. The LiDAR apparatus of claim 12, wherein the firstoptical detector and the second optical detector are each a balancedoptical detector.
 14. The LiDAR apparatus of claim 12, wherein the firstoptical arrangement further includes at least one optical deviceconfigured to route the single spatial mode optical beam from the firstbeam splitting component to the lensing optics, and route the firstreturn optical beam from the lensing optics to the second beam splittingcomponent.
 15. The LiDAR apparatus of claim 12, wherein the lensingoptics include distinct first and second lensing optics configured torespectively transmit the single spatial mode optical beam towards thetarget, and collect the light incident upon the target into the returnpath, the light being collected into the first return optical beam. 16.A method of light detection and ranging, the method comprising: emittingrespectively a first optical beam and a second optical beam that haveopposite polarizations; combining the first optical beam and the secondoptical beam into a single spatial mode optical beam; and splitting thesingle spatial mode optical beam into a plurality of single spatial modeoptical beams.
 17. The method of claim 16, further comprising: splittingthe first optical beam into a first high-power path optical beam and afirst low-power path optical beam; and splitting the second optical beaminto and a second high-power path optical beam and a second low-powerpath optical beam.
 18. The method of claim 17, further comprising:transmitting a first single spatial mode optical beam of the pluralityof single spatial mode optical beams toward a target.
 19. The method ofclaim 18, further comprising: collecting light incident upon the targetinto a return path, the light being collected into a first returnoptical beam; splitting the first return optical beam into a firstspatial mode optical beam and a second spatial mode optical beam; anddetecting respectively a first beat frequency of a combination of thefirst spatial mode optical beam and the first low-power path opticalbeam and a second beat frequency of a combination of the second spatialmode optical beam and the second low-power path optical beam.
 20. Themethod of claim 18, wherein a first single spatial mode of the pluralityof single spatial mode optical beams is transmitted toward a firsttarget by a first optical arrangement and a second single spatial modeof the plurality of single spatial mode optical beams is transmittedtoward a second target by a second optical arrangement.